Velocity threshold for cast rifle boolits.

[MBTcustom]

Me thinks most all are beginning to understand the RPM threshold and what is really occurring. Even Leftiye is on the right track as what occurs during internal ballistics (acceleration) to upset the cast bullets balance (no matter how carefully we cast and loaded it to maintain balance and concentricity) is exactly what the centrifugal force acts more forcefully on as the RPM (velocity with a given twist) is increased. Gear and Goodsteel are all over it because it's what we do to keep the bullet balanced as we increase the RPM/velocity in a given twist barrel that determines where the RPM threshold will be. Using a slower twist, if one has the opportunity, certainly is a benefit as it keeps the RPM lower and the adverse effect of the centrifugal force lower at higher velocity.

357maximum

Yes, I briefly flirted with Edd's alloy before I began the move from Washington to Arizona a year and a half ago (where does the time go.....). I met with almost immediate success boosting the 311466 from the 27.5" Palma barrel at 2600 fps/40,000 psi to almost 2700 fps with 43,000 psi (taking that off the top of my head just for conversation here-would have to research the records for the actual data). Accuracy remained the same with 1.2 - 2 moa 10 shot groups at 200 yards.

The initial problem I ran into was simply I was out of case capacity in the .308W. Faster powders for increased velocity also increased the psi. Slower powders simply did not give even the 2600 fps so while the psi was lower so was the velocity. Solution; a larger case capacity. Hence the interest in this 30x whatever cartridge in the 14 or 16" twist barrel. I believe it can contain enough RL19, AA4350 or H4831SC at close to 100% case capacity to maintain 40 - 43,000 psi and 2700 - 2800 fps out of the 26" barrel with 150 - 160 gr cast bullets.

Note the 26" barrel minimum I am getting for this cartridge; as mentioned muzzle exit pressure is very important. The longer the barrel the higher the velocity can be with less muzzle exit pressure. Several have posted or PM'd me asking about short barrels with slow twists getting higher velocities. The requests have revolved around 18 - 20" barrels but even a 16" barrel was considered. I try to explain that those HV, even with a slower twist, will necessitate faster burning powders, higher time/pressure curves and thus higher muzzle exit pressures. With a proper ternary alloy cast bullet the shorter barrels become a very difficult obstacle to overcome. Just part of all the things we must consider if we are to keep the bullet as balanced as possible to push it to higher velocity before it bumps into it's RPM threshold.

Larry Gibson

You know Larry, I can't build you a rifle if you don't visit the P.O. once in a while

Everything on earth has an RPM threshold. I know this very well from dealing with air bearings. There is a point where things fly apart no matter what they are made of. Air bearings are a very curious thing. Especially the ones that are used in the dentist office. Those drills spin at 400,000 RPM and that is no little feat. I have tried to make an air bearing from scratch because I was fascinated with the way it functions, because the internal parts ride on a cushion of air, which allows nearly effortless motion.

So I set about to build an air bearing. I precision ground all the parts, and worked for weeks on it. I finally got it to float, but it would support no weight, and would crash if it was spun. Considering that, the dental tools that are found in every single dentistry in the nation, functions in a very narrow limit of parameters. There is nothing easy about it! One fleck of dust, one ten thousandth of an inch in the wrong place, and it wont even try to work, yet they are found in every town in the nation.

The point is, we are surrounded by much more difficult things than shooting a lead boolit at high speed through a precision barrel. I really think that if you posed this question to a bunch Boeing engineers and scientists, and made it their mission in life to make a cast lead boolit fly as fast as possible while maintaining accuracy, they would probably deliver 3000 FPS out of a 10 twist with 1/2 MOA accuracy. If you knew the hoops they jumped through to bring you such novel inventions as the jet engine, you would be duly impressed.
The problem is, we're loading janky boolits, in janky brass, shooting them in janky barrels, that are screwed into janky rifles, and wondering why we can't get them faster.

Personally, I think a lack of precision across the board is jerking the rug out from under us every time. It really is like trying to sign your name with a fountain pen that has been duct taped to the end of a broom handle.

I see the RPM threshold as a measure of boolit perfection. I mean, if you could get a perfect boolit out of the dad-burned barrel, there's really no reason why it can't be pushed way up there in speed. If the boolit was perfect, and unmolested, I would think that the true RPM threshold of water dropped WW alloy would be about 3900 fps. At that point, the lead would literally fly apart from the g-forces imparted on it.

[9.3X62AL]

Ha ha, Dan--if it was only that simple a question.

I wholly accept the premise that a rifle chamber/throat/barrel is a very hostile environment to a relatively-soft item like a cast boolit, even one of Linotype metal and corresponding very closely to throat and barrel dimensions. That question seems to be the Big One, and how to manage those forces arrayed to ruin the casting. There were very sound reasons that the military establishments went to gilding metal jackets on their rifle projectiles very soon after smokeless powder's increased velocity potential was realized. The commercial and sporting venues followed suit, again for good reasons. This wholesale reliance upon the red-coated bullet for rifle usage has caused lead bullets and the hobbyists who persist in their use in rifles to be viewed as curiosities. I well recall a varmint hunt some years ago with Buckshot, in which I was using RCBS castings in my Rem 788 x 243. A couple hunters stopped to talk, and the conversation drifted into calibers and bullets in use. Rick mentioned that I was using a cast bullet in the centerfire rifle, and the look on one guy's face was as if Rick lapsed into Serbo-Croatian. The poor benighted soul couldn't get his mind around it. Those castings at 1700 FPS or so really tagged out the ground squirrels right smartly, too.

[45 2.1]

No mystery at all......... Whats been done has been out there for the last 120 years. Less drama please. Shoot your rifles and report the results so we can see if the rhetoric is warranted.

[Piedmont]

I'm having trouble understanding why muzzle pressure matters. It seems to me if the crown is right that the bullet wouldn't be destabilized. What am I not grasping?

[Larry Gibson]

........I see the RPM threshold as a measure of boolit perfection. I mean, if you could get a perfect boolit out of the dad-burned barrel, there's really no reason why it can't be pushed way up there in speed. If the boolit was perfect, and unmolested, I would think that the true RPM threshold of water dropped WW alloy would be about 3900 fps. At that point, the lead would literally fly apart from the g-forces imparted on it.

There in lays the rub; getting a "perfect" bullet out of the barrel. Accelerating a cast bullet with it's attendant elastic/plasma properties to 2600+ fps inside an effective barrel length of 22 - 24" without deforming/unbalancing it seems to be the problem........

Larry Gibson

[MBTcustom]

Indeed! but I still hold that there is much that can be done to make that happen that is not being done.
I'm going to run my own experiments once I get my own 30XCB-ish rifle built, and we'll see what we shall see. I'm able to change the basic makeup of a rifle's chamber at a whim, so I might be able to learn something that has not been discovered (recently anyway's LOL!).
I'm excited to see what can be done, pushing to the limits.

[badgeredd]

I'm having trouble understanding why muzzle pressure matters. It seems to me if the crown is right that the bullet wouldn't be destabilized. What am I not grasping?

I suggest that you demonstrate the effect of muzzle pressure to yourself by doing a little experiment. I suggest something 30 caliber or smaller. Use a medium capacity rifle cartridge and load it to a reasonable (meaning medium) velocity using the same bullet but three different powders. Use a fast powder, a medium rate powder and a slow powder and load the cartridges to the same velocity. Shoot the three loads on paper and compare the groups. I'd be surprised if you don't see the difference in groups. I've usually seen a marked difference as the muzzle pressure increases.

Edd

[TXGunNut]

I have offered so many times I made it a long standing offer for any of you boys to show me how it's done (casting, loading and shooting cast bullets out 7 - 10" twists rifles at high velocity of 2200+ fps with linear accuracy of 2 moa or less out to 300 yards)....Larry Gibson


Thanks, Larry. I thought I was doing something wrong. I'm relatively new at CB's but I'm brutally honest about my results and I have pretty high (too high) standards for hunting accuracy for the conditions I hunt in.

[runfiverun]

man OH man there are a LOT of clues as to what is needed in the last couple of pages.


Larry is on the same track i was following when i mentioned cutting the 30 xcb to Tim,Ian etc. the first time.
I was starting to really stretch my 10 twist 308 using H-4831sc.
i was beginning to look at pressure time curves and altering them with different powders on top of and below the 4831.
everything else HAS to be correct before you get that far along.
and by everything else i mean bore alignment and throat fit, without those you can change powder from bullseye through H-860 without any better results.

[DanWalker]

WOW! What a wonderfully interesting can of worms I have opened... To boil my question down, How slow can these MIhec 30 caliber FN boolits decellerate to and retain their magic, before they just poke a hole and I have to go "A trailing" to find my critter?

[Larry Gibson]

WOW! What a wonderfully interesting can of worms I have opened... To boil my question down, How slow can these MIhec 30 caliber FN boolits decellerate to and retain their magic, before they just poke a hole and I have to go "A trailing" to find my critter?

It's not that difficult Dan. Here's a repost of #43 in this thread. It tells you how I do it and also you can "search" for BruceB's method which works fine also. I use a softer alloy (COWWs +2% tin and then mix with lead at 50/50) and AC the bullets. I also use a 1/8" Forster HP tool to HP the bullets (if the mould is not an HP mould) to 3/16" deep. I find that a retained velocity of around 1500+ fps gives sufficient velocity for decent expansion out to 200 yards. That generally means a muzzle velocity of 1900 - 2200 fps depending on bullet design, the cartridge, the barrel length and the barrel twist used. The soft alloy and smaller HP allow for controlled expansion at close ranges w/o so called bullet "blow up". Been using the such on .30 cal, 8mm, 35, .375 and .45 cal cast for many years with 100% success.

Dan

Sorry for getting the thread off track. I answered your question as to why the accuracy was different at different velocities. Every time I give that correct answer (it is ballistic science) the pundits come out as we see. Their response doesn't alter the facts of what you have found and the real reason for the cause of it.

The fact is a softer cast bullet at 1800 - 2200 fps is indeed and excellent killer of medium game. It is easy enough to get very good hunting accuracy with such softer cast bullets in the 2000 - 2200+ fps range with rifles having 12 - 16" twist barrels depending on caliber. With faster twist barrels 1800 - 1950 fps is very doable. My own preference gives me a max range of 200 yards on deer size+ game as I want enough retained velocity for expansion. That seams to be in the 1400 - 1600 fps range with the alloy I mentioned earlier. Thus with cartridges in barrel twists I can get sufficient hunting accuracy at the max range (just because a load seems to shoot good at 50 yards is no guarantee it will shoot with sufficient accuracy at your max range) I find 200 yards to be an excellent practical limit for those with 2000 - 2200 fps.

BruceB's composite bullets also work very well and I've used them with success also. I've just been cast the soft ones so long it comes easy. They are easy to load and use (just have to cleaned the barrel every 7 shots or so to maintain the best accuracy which is ok for hunting bullets. They also work extremely well on the terminal end. Which ever way you go you are on the right track.

Larry Gibson

[rosst]

so how fast can someone push a boolit accurately with a short 20 inch barrel in .308 before exit pressure upsets things . . . any thoughts

cheers R.

[Dutch4122]

so how fast can someone push a boolit accurately with a short 20 inch barrel in .308 before exit pressure upsets things . . . any thoughts
cheers R.

The key here is to use heavier boolits in the shorter than normal barrel. In the .308 Winchester I have had my best results with the 210 grain 314299.

I have a Spanish FR-8 Mauser in 7.62x51 Nato, which has less than 20" of useable barrel and is fitted with an "AR" style muzzle break. My load is 45 grains of IMR-4007ssc pushing the 210 grain slug at a chronographed 2,180 fps. I would suggest going with powders of the same burn rate as IMR-4007ssc and faster; such as IMR-4320, IMR-4064, and IMR-3031.

The key here with muzzle pressure is that a faster burning powder will yield a lower muzzle pressure that a slower burning powder. Using a heavy for caliber boolit with a slower burning powder will also cause a more efficient powder burn sooner in the barrel thus yielding lower muzzle pressures. My experience has shown that lower muzzle pressures translate to better accuracy with cast boolits.

Also, a longer barrel will produce lower muzzle pressures with any given powder than a shorter barrel.

Hope this helps,

[MBTcustom]

WOW! What a wonderfully interesting can of worms I have opened... To boil my question down, How slow can these MIhec 30 caliber FN boolits decellerate to and retain their magic, before they just poke a hole and I have to go "A trailing" to find my critter?

You did indeed get a rousing discussion started! I am exceedingly curious about high velocity shooting just because it's kewl and "just that simple, just that hard".
However, if all your doing is hunting, then make sure when your 50/50 water dropped blobs of silvery sweetness hit yon critter, they are going at least 1200FPS. I underestimated the power of a high speed, soft boolit last year (see my sig line). if all you're doing is filling the freezer, then keep it slow and accurate, and kill 'em with kind, and gentlemanly accuracy. 1600fps is a good even number that will stack deer up like dominoes, so make sure the boolit is crossing the crown of your rifle at about 1800fps and you got it in the bag.

[geargnasher]

The key here is to use heavier boolits in the shorter than normal barrel. In the .308 Winchester I have had my best results with the 210 grain 314299.

I have a Spanish FR-8 Mauser in 7.62x51 Nato, which has less than 20" of useable barrel and is fitted with an "AR" style muzzle break. My load is 45 grains of IMR-4007ssc pushing the 210 grain slug at a chronographed 2,180 fps. I would suggest going with powders of the same burn rate as IMR-4007ssc and faster; such as IMR-4320, IMR-4064, and IMR-3031.

The key here with muzzle pressure is that a faster burning powder will yield a lower muzzle pressure that a slower burning powder. Using a heavy for caliber boolit with a slower burning powder will also cause a more efficient powder burn sooner in the barrel thus yielding lower muzzle pressures. My experience has shown that lower muzzle pressures translate to better accuracy with cast boolits.

Also, a longer barrel will produce lower muzzle pressures with any given powder than a shorter barrel.

Hope this helps,

Muzzle pressure and ignition consistency/repeatability create a paradox. That's where the handloader's work really gets cut out for them. Launching a boolit out of the case with a stiff charge of fast/medium powder comes with a lot of challenges, and having excessive muzzle pressure with the slower powders does too. I spend a lot of effort playing games to overcome this, but it's worth it each time I figure out a new trick or approach to the problem.

Gear

[DanWalker]

It's not that difficult Dan. Here's a repost of #43 in this thread. It tells you how I do it and also you can "search" for BruceB's method which works fine also. I use a softer alloy (COWWs +2% tin and then mix with lead at 50/50) and AC the bullets. I also use a 1/8" Forster HP tool to HP the bullets (if the mould is not an HP mould) to 3/16" deep. I find that a retained velocity of around 1500+ fps gives sufficient velocity for decent expansion out to 200 yards. That generally means a muzzle velocity of 1900 - 2200 fps depending on bullet design, the cartridge, the barrel length and the barrel twist used. The soft alloy and smaller HP allow for controlled expansion at close ranges w/o so called bullet "blow up". Been using the such on .30 cal, 8mm, 35, .375 and .45 cal cast for many years with 100% success.

Dan

Sorry for getting the thread off track. I answered your question as to why the accuracy was different at different velocities. Every time I give that correct answer (it is ballistic science) the pundits come out as we see. Their response doesn't alter the facts of what you have found and the real reason for the cause of it.

The fact is a softer cast bullet at 1800 - 2200 fps is indeed and excellent killer of medium game. It is easy enough to get very good hunting accuracy with such softer cast bullets in the 2000 - 2200+ fps range with rifles having 12 - 16" twist barrels depending on caliber. With faster twist barrels 1800 - 1950 fps is very doable. My own preference gives me a max range of 200 yards on deer size+ game as I want enough retained velocity for expansion. That seams to be in the 1400 - 1600 fps range with the alloy I mentioned earlier. Thus with cartridges in barrel twists I can get sufficient hunting accuracy at the max range (just because a load seems to shoot good at 50 yards is no guarantee it will shoot with sufficient accuracy at your max range) I find 200 yards to be an excellent practical limit for those with 2000 - 2200 fps.

BruceB's composite bullets also work very well and I've used them with success also. I've just been cast the soft ones so long it comes easy. They are easy to load and use (just have to cleaned the barrel every 7 shots or so to maintain the best accuracy which is ok for hunting bullets. They also work extremely well on the terminal end. Which ever way you go you are on the right track.

Larry Gibson

Thanks!

[TCLouis]

45 2.1

Looks like you and I use the same exploding vs splitting milk jug test.

I just have not gotten the chance to test those loads that explode milk jugs on live game to prove my theory.

I used this method because of the jug impact reactions of coated bullet loads at adequate velocities vs cast.
I have found some nice flat point cast bullets cause the jugs to EXPLODE at "relatively" low velocities.

[Larry Gibson]

Muzzle pressure and ignition consistency/repeatability create a paradox. That's where the handloader's work really gets cut out for them. Launching a boolit out of the case with a stiff charge of fast/medium powder comes with a lot of challenges, and having excessive muzzle pressure with the slower powders does too...........Gear

Indeed the "paradox". Getting higher velocities out of shorter barrels is indeed harder than with longer barrels which is why I always recommend the longer barrel. Attaining higher velocities with cast in the shorter barrels is a balancing act between preventing as much damage (sloughing, bending, uneven obturation, etc.) to the bullet during acceleration and keeping the pressure low enough at the muzzle so accuracy in not adversely affected. Another reason why I so often recommend powders from 4895 to RL22; specifically those within that burning range with proven ignition reliability at the lower psi's we use with cast bullets.

To answer rosst's question; if all is done correctly then sometimes 2000 - 2100 fps can be attained (obviously a 12" twist barrel is going to do it easier than the 10" twist barrel in .308W) but I've found the norm is usually 1900 to 2000 fps before non linear group dispersion appears. If you are hunting and shots are 100 yards or under then very usable hunting accuracy is attainable in the 2100+ fps range.

Larry Gibson

[shredder]

There is so much information on this thread it is hard to grasp it all. A long convuluted trail but some heavy hitters have weighed in here with personal observation and experimentation. That makes this a thread to print out, hole punch, and read over slowly at leisure.

This is almost a stickie.

[felix]

Yep, it is a genuine balancing act. Also, include in analysis where the maximum pressure point occurs within the barrel. Most important is the shape of the acceleration curve at the peak pressure point. The pointer the curve, the more sharply defined the impulse generated, which translates to a sharper vibe peak, which then moves the barrel sharper, which then makes the group larger. The paradox, a'la' Ian, is therefore magnified when groups are more important than point of impact. ... felix